Graffiti vandalism in public transit systems and city neighborhoods is a serious problem. While public transit authorities and city governments have largely conquered paint and ink graffiti, a new type of graffiti vandalism has emerged—the scratching/etching of polycarbonate and glass windows, called “scratchitti.” As with the paint and ink graffiti, “scratchitti” damages the external appearances of structural materials. However, unlike paint graffiti, the scratches cannot be removed or hidden and cause permanent damage.
Scratchitti vandalism is a major problem for the New York City Transit (NYCT) System, which currently operates 5,792 passenger railcars and provides service 7 days a week, 24 hours a to approximately 1.1 billion riders a year. NYCT has operated a graffiti free fleet since May 1989. They can remove paint or ink graffiti markings from cars within twenty-four (24) hours. However, they cannot correct the damage from the scratches/etches on polycarbonate and glass windows, samples of which are shown in FIG. 1. Currently, the prevalence of scratchitti is high; it is believed to be on almost every window and door of every rail car of New York City's (NYC) subway lines. NYCT has approximately 174,000 pieces of glass in the subway fleet. It has been estimated that to run a scratch-free fleet, NYCT would have to spend $60-70 million per year to replace window and door glass. At the present time, NYCT replaces glass only when it is too scratched to see through, or when it has obscenities or racial slurs etched into it. In 1997, NYCT replaced approximately 62,000 pieces of damaged glass for a material and labor cost of $2.6 million.
Scratchitti is not limited to subways. Windows and doors (often large and expensive) of private cars, public buses, bus shelters, residential homes, and business buildings also suffer severely from this type of vandalism. Without an easy method for removing this graffiti, property owners face a costly situation. Scratches to glass or polycarbonate panels may take months to remove using ordinary methods, and some require major engineering efforts costing thousands of dollars.
The present invention presents an environmentally benign and novel re-manufacturing process for removing scratches in planar panels of translucent or transparent materials including glass and possibly polycarbonate. This invention allows damaged windows/doors to be reused, thereby eliminating waste disposal of replaced glass. By effectively removing scratches, the process reduces disposal and replacement costs, saves natural resources, and helps to create a more pleasant living environment. This process can also help to improve safety, as it is appropriate for renewing the surface wear of canopies of aircraft and machinery.
In the early 1980s, polycarbonate windows were first installed in railcars and solved the problem of glass window breakage. However, it was discovered that polycarbonate panels could be easily scratched with anything from knives to paper clips. Vandals made heavy use of this new medium, and polycarbonate windows were being replaced in epidemic proportions. Later, a new type of impact resistant glass that met FRA requirements and was more resistant to scratches was developed and installed on the railcars. Although this new type of glass is more scratch resistant, vandals also modified their art using tools ranging from emery cloths to diamond dust encrusted pen styluses to scratch these new windows. Since manufacturing unscratchable glass is technically impossible, many organizations have investigated potential methods to remove the scratches, such as grinding/polishing the scratches, applying plies of Mylar film (polyester film) to the glass, and patching with clear polymer coating. To date, no readily-workable solution has been identified.
Grinding/polishing operations require that the panel be removed from the frame for the scratches to be polished out. Attempts to polish/grind the scratches at NYCT facilities were very labor intensive. Thus the windows are instead shipped to a vendor who polishes the panel to remove the scratches. However, deep scratches cannot be removed without impairing the integrity of the panel. This process requires removing the damaged window and replacing it with a new or repaired window, accruing labor, material, and storage costs.
The process of covering windows with plies of Mylar (polyester) film is slightly more beneficial. The film can be applied to the window while it is in place in the frame. For the most part, the film protects the window pane from being scratched. However, because the film itself is more susceptible to scratching than the glass, it must be replaced often, which again results in a material and labor costs. Moreover, this approach cannot restore glass windows already scratched or etched.
When epoxy or polyurethane coatings are applied to the glass, scratches are successfully filled in and seemingly disappear. However, the window has to be removed from the frame because the coating must be applied to the glass when it is in a horizontal position. Applying the coating vertically results in the material dripping and running. The coating also must be applied in a clean environment to prevent dust and dirt from being embedded in the coating, which means the windows must be shipped to the vendor, having clean room facilities. When the coating becomes scratched, the window again must be removed, and to ensure compliance with flammability regulations, the first coating is removed before another coating is applied. Again this is a labor and material-intensive process.
Based upon the above prior art, optimum requirements for a workable solution to the “scratchitti” problem include:                Optimally, glass repair should be carried out while the glass is in the frame on the railcar, building or other structure;        The repair/protection process should not be labor intensive and should allow for completion within a period on the order of a fraction of an hour;        If the window must be removed from the frame the repair/replacement time should be less than one hour;        The repaired/protected glass must be able to fit back into the window frame;        The structural integrity (impact resistance, strength) of the glass should not be substantially impaired by the repair/protection process;        The optical quality of the treated glass should not be substantially different from that of the original glass;        There should be no substantial distortion, dripping, or running of panel materials;        Any coating used must meet flammability and smoke toxicity requirements;        The repair/protection process should not add significant weight to the panel;        Any coating/film used should not be readily detectable—no edges should be apparent;        The protective process should substantially maintain the scratch resistance of the original panels;        Any coating/film used should be resistant to the cleaners and solvents used to clean and maintain the surfaces.        
The prior art is not believed to meet these optimal needs.